1. Field of the Invention
The present invention relates to an interunit communication system for executing a communication between a main unit and one or a plurality of subunits which are controlled by the main unit and also relates to a method of resetting the subunits by the main unit.
2. Related Background Art
Hitherto, in such a kind of system for executing the interunit communication, power source lines, communication lines, resetting lines, and other signal lines are individually provided and a plurality of lines are combined and the units are connected. On the other hand, there also exists a system in which in order to omit the resetting lines among the above lines, each subunit has therein a circuit to individually reset an included microcomputer.
However, in the system in which in order to reset the microcomputer in the subunit, a plurality of lines including the resetting line are combined to connect the units, in addition to a drawback that the combining cost is necessary, there is a large drawback such that in the case where noises were mixed onto the resetting line, the microcomputer in the subunit is reset by the noises.
On the other hand, in the system in which the resetting line is omitted by providing the resetting circuit in the subunit, if the microcomputer in the subunit runs away, there is no means for detecting such a microcomputer runaway and for automatically resetting the microcomputer. Therefore, each device in the subunit that runs away, results in serious damage to the apparatus. To stop the runaway, a runaway detecting circuit must be provided for each subunit. There is a drawback that when the number of subunits increases, the cost of the runaway detecting circuits substantially increase.